The invention is based on an oil separator for crankcase gases of an internal combustion engine, comprising a preliminary separator, a cyclone separator, a fine separator and, if necessary, a valve device that are provided in a cascade arrangement on a cylinder-head hood of the internal combustion engine.
When an internal combustion engine operates, streams of blowby gas are produced between pistons, piston rings, and cylinder walls and, if applicable, in the region of valve guides. This blowby gasxe2x80x94which enters the crankcase or a camshaft housing, or travels above the cylinder head or is guided therexe2x80x94contains fluid components, primarily fine oil droplets or motor oil components with a low boiling point. Larger oil droplets can also be contained in the crankcase gas or even in the camshaft housing gas that are produced by moving drivetrain parts, i.e., piston, connecting rod, crankshaft or camshaft. This is also referred to as xe2x80x9cswirl oilxe2x80x9d. In order to remove the blowby gases, a venting of the crankcasexe2x80x94which usually extends over the camshaft housingxe2x80x94is provided. These gas/fluid quantities referred to as crankcase gas and occurring intermittently are separated from the fluid components by means of an oil separator and then typically directed to the intake region of the internal combustion engine. By separating the oil, dirt is prevented from accumulating in the downstream regions, and the emission of hydrocarbons is not increased in an undesired fashion.
An oil separator for crankcase gases of the generic type is made known in DE 197 00 733 A1. This publication discloses and teaches that the components of the oil separator named initially are to be located in the cylinder-head hood of the internal combustion engine. The preliminary separator and the cyclone separator are located on the inside of the cylinder-head hood, i.e., on the side of the cylinder-head hood facing the crankcase and/or camshaft housing. The fine separator and the valve device are located between two housing cover halves of the cylinder-head hood and are located downstream from the cyclone separator in terms of flow.
The known means of attaining the object of the invention entails a great deal of integration expense in terms of structurally locating the oil separator components in the cylinder-head hood. It is also very tall. Integrating it therefore depends to a large extent on the specified and always different design of the cylinder-head hood.
Based on this, the object of the present invention is to improve a generic oil separator of the known type to the extent that it is simplified in terms of design engineering and can be used with a larger number of cylinder-head hood designs.
This object is attained according to the invention with a generic oil separator by locating the preliminary separator, the cyclone separator, the fine separator and the valve device provided, if necessary, on the ouside of the cylinder-head cover, and covering them with a housing half-shell which, together with the outside of the cylinder-head hood, forms a housing for the oil separator and can be installed against the outside of the cylinder-head hood in sealing fashion. Protection is also claimed for a cylinder-head hood having an oil separator, according to the invention, mounted to the outside.
With the invention it is also proposed to locate the components of the oil separator outside the cylinder-head hood itself. This opens up the possibility of producing all components in one housing, i.e., a housing half-shell of the oil separator, as a subassembly that can be pre-assembled, and then adjoining this subassembly in entirety, in modular fashion, with or without an additional bottom part, to the outside of the cylinder-head hood. In particular, the cylinder-head hoodxe2x80x94detached from components of the oil separatorxe2x80x94can be installed on the cylinder head in order to seal off the top of the camshaft housing. The preassembled subassembly of the oil separator can then be installed at this time or a later time.
It is found to be particularly advantageous when the housing half-shellxe2x80x94which forms a housing for the oil separatorxe2x80x94is a plastic part produced as a single component, in particular an injection-molded part.
With regard for the ability of the oil separator to be preassembled in specific subassemblies, it is found to be particularly advantageous when flow guide walls of the preliminary separator, a helical insert for the cyclone separator, a separator insert for the fine separator, and preferably the valve device as well, can be placed in the housing half-shell for preassembly. All components with regard for the housing half-shell can then be preassembled, stockpiled as ready-to-install subassemblies, and then delivered to the cylinder-head hood at the desired point in time for final assembly.
The housing half-shell should be advantageously designed rather flat and elongated in shape. To handle crankcase gases of up to 150 l/min, a diameter of only approximately 295xc3x9760xc3x9770 mm (lengthxc3x97widthxc3x97height) has been found to be sufficient; with this, it was possible to separate oil quantities of 100 to 200 g/h. In order to obtain these quantities using non-generic, modular designs of externally adjoined cyclone separators, a much greater overall height of 175 mm and a length and width of 105xc3x9790 mm was required until now. The design according to the invention makes it possible to realize pancake-designed, elongated dimensions when configuring the oil separator in the range described hereinabove, which said dimensions are sufficient in terms of their efficacy, throughput rate, and separation capacity.
It is found to be advantageous when the housing half-shell comprises circumferential side walls extending in the direction toward the cylinder-head hood that transition into a full-perimeter, front edge facing the cylinder-head hood, with which the housing half-shell can be placed against the outside of the cylinder-head hood in sealing fashion.
This full-perimeter, front edge can advantageously define a seating plane, which then makes it necessary to design the outside of the cylinder-head hood correspondingly flat in the region where the oil separator is installed. A design of the housing half-shell of the oil separator having circumferential side walls extending in the direction toward the cylinder-head hood, i.e., having a substantially pot-shaped geometry, makes it possible in particularly advantageous fashion to preassemble all components in the protected and prefabricated housing, which then only need be joined with the outside of the cylinder-head hood via its full-perimeter edge. As an alternative or in addition, a bottom part could close the housing half-shell of the subassembly, in particular except for afflux and return openings.
The adjoining of the housing half-shell to the cylinder head-hood can be realized via lugs projecting laterally from the housing half-shell and integrally molded in particular as a single component to the housing half-shell, which lugs are then advantageously penetrated by screws that can be screwed into corresponding thread openings in the top of the cylinder-head hood. These thread openings can be formed in particular by dome-shaped raised areas on the outside of the cylinder-head hood. In the case of this exemplary embodiment, the lugs are reset behind the front edge of the housing half-shell in the direction of installation of the housing half-shell. During installation, the dome-shaped raised areas on the outside of the cylinder-head hood then form installation and centering aids during adjoining and correct positioning of the preassembled subassembly. The lugs can forms seating surfaces when the screws are tightened, which ensure correct installation. A fastening means using plastic snap-in hooks is also feasible and advantageous.
Moreover, it is found to be advantageous when the flow path is redirected substantially at a right angle downward in the direction toward the outside of the cylinder-head hood between an upwardly-opening outlet of the fine separator, i.e., in the flow direction after an outlet opening of the fine separator insert, e.g., a thread spool, and an outlet of the oil separator toward the intake device of the internal combustion engine. Due to this redirection-twice, at right angles, in particularxe2x80x94during emergence, as compared with an arch-shaped diversion at the level of the outlet opening of the fine separator insert (as with DE 197 00 733 A1) of the fine separator, a reduction in length, particularly by up to 20 mm, is obtained. This is referred to as a steeply-designed transfer passage between the fine separator and an outlet region of the oil separator, where the valve device for pressure regulation and limiting the crankcase gases is also provided.
In building on this inventive idea, it is found to be advantageous when a recess in the form of a necessarily provided volume of the housing half-shell is provided between a housing region enclosing the fine separator and a housing region of the housing half-shell enclosing the outlet and/or the valve device, i.e., underneath the transfer passage mentioned hereinabove, into which said recessxe2x80x94when the oil separator is installedxe2x80x94an opposed shape of the top of the cylinder-head hood-designed complementary in shape-engages. Due to this engagement, a dead volume is prevented in which oil can collect since it is the lowest point in the oil separator. This prevents a situation in which, when the engine position changes during driving, a large quantity of oil can be directed from there to the induction tract and, therefore, back to the combustion chamber.
In the case of the known oil separator according to DE 197 00 733 A1 mentioned initially, an oil return opening into the camshaft housing is formed in the region below the fine separator insert of the fine separator. In this known embodiment, fluidxe2x80x94particularly oilxe2x80x94separated in the preliminary separator and the cyclone separator travel through slanted formations in the housing and enter the housing region of the fine separator and, in this third separation step, is directed together with the fluid separated there back into the camshaft housing. According to a further independent inventive idea, it is proposed that oil separated in the preliminary separator be returned directly to the engine compartment via a further return opening. This is easily possible, because a notable pressure differential does not yet exist in the region of the preliminary separator, and the quantity of fluid separated there can simply drip or run downward, and it is not carried with the flow into the preliminary separator. In this fashion, a large portion of the fluid contained in crankcase gas, i.e., larger oil droplets, are separated out in advance and returned directly to the engine compartment. The same opening in the cylinder-head hood is preferably used for the return, running-off or dripping of this quantity of fluid as well as directing the crankcase gas into the oil separator. This opening preferably has a large opening cross-section that can comprise, for example, a draining wallxe2x80x94that is domed, in particularxe2x80x94projecting into the camshaft housing compartment, which said draining wall is formed by the cylinder-head hood.
According to a further inventive idea that is independent per se, the cyclone separator comprises a helical flow path that is formed by a helix having a cylindrical internal part that is capable of being installed on the housing half-shell, whereby the cylindrical internal part defines an inner diameter Di of the helical flow path and is stockpiled in various diameters. According to this inventive idea, protection is therefore claimed for a system of an oil separator having various helical flow paths, each having a different radial depth as measured from the cylindrical internal part to an outer diameter of the helical flow path, which said outer diameter is preferably formed by the housing half-shell. It is therefore proposed, according to the invention, to provide various flow paths through various helixes having a varying inner diameter and/or having a varying outer diameter by inserting cylindrical sleeves into the housing region that forms the cyclone separator, while maintaining the outer dimension of the cyclone separator.
If one assumes a quantity of crankcase gas of approximately 65 l/min, e.g., from a diesel engine having 2 to 2.5-l piston displacement, it is found to be advantageous when the flow path is sized such that the cylindrical internal part has a diameter of approximately 8 mm, and the outer diameter of the housing for the cyclone separator is 51 mm with a helical path height (slope) of 13 mm. With a smaller quantity of crankcase gas of only approximately 50 l/min, it is found to be advantageous if the inner diameter is approximately 18 mm, in order obtain a flow rate inside the cyclone separator that is nearly as great, due to the smaller flow cross-section. With the smallest quantity of crankcase gas typically occurring, 40 l/min, an inner diameter of approximately 24 mm should be suitable, again with a helix height (slope) of 13 mm and an outer diameter of 51 mm.